The invention relates to a device for detecting steering wheel contact. The invention further relates to a method for detecting steering wheel contact by means of such device.
Apart from optical detecting systems, there are basically two options of sensory detection of steering wheel contact by capacitance and by resistance, in resistive systems, an electric signal is generated by the pressure of the hand onto the steering wheel. Influences by differently tight or less tight leather wrappings and thus different initial forces acting on the sensor impede an unambiguous sensing.
In capacitive systems, currently failure-free sensing is not yet possible or possible only with major technical expenditure. Problems such as insufficient grounding, temperature influences and sensing of the initial condition upon starting the vehicle have to be solved. Especially, the sensors strongly tend to drift. In known “open” systems in which the human body forms a capacitor electrode having a variable distance from an electrode which is fixedly arranged in the steering wheel and the evaluation of which is based on an oscillating circuit, the shift of frequency (detuning of the oscillating circuit) is measured. However, already approach of the steering wheel is frequently assessed as a contact so that reliable sensing of a true contact is not ensured.
From U.S. Pat. No. 8,836,350 B2 a method of capacitive contact sensing is known which was developed for the interrogation of touch-sensitive keyboards. Within the scope of contact sensing, the voltage at an internal capacitor of an integrated circuit which is adapted to be coupled to an external capacitor is monitored.
DE 10 2012 024 903 A1 illustrates a planar formation comprising a carrier, at least two electric functional elements and at least one seam in which the strand-type functional elements are integrated. Such planar formation is intended to be used especially in electric heating units.